JPH0221643B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnet roll used in a developing device or a cleaning device in an image forming device or recording device such as an electrophotographic copying machine or a facsimile machine.

2. Description of the Related Art Conventional developing devices of electrophotographic apparatuses that use a dry developer usually utilize the magnetic force of a magnet for conveying the developer and performing the developing action itself. Figure 1 shows a conventional example of a developing device.
The electrostatic latent image formed on the surface of the photoreceptor 1 is developed by one-component magnetic toner 4 on a sleeve 3 containing a magnet roller 2. Magnetic toner 4 is stored in a hopper 5, is applied onto the sleeve 3 by a magnetic blade 6 placed opposite to the magnetic pole (N ₁ ), and is conveyed to the developing position by rotation of the sleeve 3 in the direction of the arrow. be done. A power supply 7 applies a developing bias between the sleeve 3 and the electrode 8 on the back surface of the photoreceptor 1.

Conventionally, an isotropic or anisotropic sintered ferrite magnet has been used as the magnet roll 2 used for such purposes. However, such sintered magnets require special molding equipment for manufacturing, are easily chipped, and have a large size change during sintering, so it is necessary to subsequently grind the extremely hard surface of the magnet. In addition, since the sintering reaction takes place at a high temperature, it also has drawbacks such as consuming a large amount of energy and being heavy.

In order to improve these drawbacks, rubber or plastic magnets may be integrally molded into a roll, or
Alternatively, it has been proposed to use a plurality of magnet rolls by gluing them together, but this has not been put to practical use because the resulting magnetic force is weak.
In order to obtain rubber or plastic magnets with even stronger magnetic force, attempts were made to make these magnets anisotropic, and it became possible to obtain magnets with a maximum energy product of about 10 ⁶ Gauss Oe. The magnetic force is still somewhat insufficient for use as a magnet roll in a developing device for photographs, etc.

An object of the present invention is to produce a magnet roll that can obtain strong magnetic force using a rubber magnet or a plastic magnet.

In order to increase the magnetic flux density of a developing magnetic pole that requires a particularly strong magnetic flux density in, for example, an electrophotographic developing device, the present invention is directed to arranging magnets so as to have mutually repelling magnetic forces and adhering them to a support shaft. This constitutes a magnetic roller. In particular, by arranging the easy magnetization axes of other magnetic poles adjacent to the magnetic pole to be strengthened so as to be substantially perpendicular to the adjacent surface, a copolarity effect is obtained and a strong magnetic field is generated. It is preferable to use an anisotropic rubber or plastic magnet rather than an isotropic one because a stronger magnetic force can be obtained.

Embodiments of the present invention will be described in detail below with reference to the drawings.

A composition containing 80 to 95 parts by weight of barium ferrite and strontium ferrite as plastic magnets, with the remainder being vinyl chloride and chlorinated polyethylene/ethylene vinyl acetate copolymer, is heated and kneaded in a roll mill, and then pulverized in a pulverizer. When extruding the pellets and processing them into long objects, a magnetic field was applied using an electromagnet to create a magnet, and the maximum energy product was
A magnet of 1.1×10 ⁶ Gauss・Oe was obtained. Furthermore, a rubber magnet formed by mixing nitrile rubber and ferrite can also be used.

Put a plurality of these magnets together and attach them to the support shaft 9.
They were bonded together with an adhesive to form a magnetic roller 2 having a support shaft diameter of 7 mm, a roll outer diameter of 25 mm, and a length of 300 mm as shown in FIG.

Comparative Example FIG. 3a is a side view of a magnet roll 2. Four magnets prepared as described above were laminated on a shaft 9 with N and S poles alternately to obtain a magnet roll. The arrows shown in each of the magnets 2a to 2d in FIG. 3a indicate the orientation direction of the easy axis of magnetization of the magnet. When we measured the magnetic flux density on the surface of the magnet roll with the orientation direction of the easy axis of magnetization selected in this way, we found that each pole had a maximum of 1000 G (Gauss), which is larger than the conventional isotropic magnet roll, but still This was insufficient for use as a magnet roll for an electrophotographic developing device. Figure 3b shows the state of the magnetic field at this time.

Example 1 Next, the magnet roll to which the present invention is applied was
Shown in Figure a.

In FIG. 4a, each magnet piece 2a, 2b,
2c and 2d form N ₁ , S ₁ , N ₂ and S ₂ poles, respectively, and the easy magnetization axes of each magnet piece 2a to 2d are oriented as shown by the arrows.

When the magnet pieces are arranged in this way, the magnet pieces repel each other, but by adhering the magnet pieces against this repulsive force, a strong magnetic force can be obtained. That is, in the case of the _N1 pole, the axis of easy magnetization of the magnet piece 2d adjacent to the magnetic piece 2a, which mainly forms the magnetic field of the _N1 pole, is almost perpendicular to the adjacent surface 10 of both magnets. In addition, the lines of magnetic force passing through the magnet piece 2d also pass through the inside of the magnet piece 2a, resulting in a commutating pole effect. Since a commutating effect is obtained for each magnetic pole in this way, the lines of magnetic force that are formed are concentrated on the adjacent surface 10 side for the _N1 pole, for example, as shown in FIG. 4b, and a strong magnetic field is therefore formed. In this way, we were able to obtain a maximum of 1150G for each pole.

Example 2 In order to further enhance the interpolation effect as described above, the fifth
As shown in figure a, each magnet piece 2a, 2b, 2c,
2d were bonded together to form N ₁ , S ₁ , N ₂ , and S ₂ poles respectively. The easy magnetization axes of each of the magnet pieces 2a to 2d were oriented as shown by the arrows.

By arranging the magnet pieces in this way, the magnetic field of _the N ₁ pole is mainly formed by the 2
For the magnet piece a, the adjacent magnet piece 2b,
Since the axis of easy magnetization of the magnet piece 2d is almost perpendicular to the adjacent surfaces 11 and 12 of the respective magnets, each has a commutating effect, and the lines of magnetic force are N 1 poles and ₁ poles as shown in Fig. 5b. Concentrate on N ₂ poles, N ₁ pole and
The maximum surface magnetic flux density of each _N2 pole was 1250G.

Moreover, the surface magnetic flux density of the S ₁ pole and S ₂ pole is reduced to 800 G compared to the comparative example shown in FIG. 3a.
However, in general, in a magnet roll for an electrophotographic developing device, the magnetic pole fixed at the developing position requires a relatively strong magnetic flux density, but the other poles do not have much trouble even if they are weaker than the developing magnetic pole. Attach the non-magnetic sleeve 3 to the outer circumference of the magnet roll 2 as shown in Figure 6, and attach the non-magnetic sleeve 3 to the arrow A.
When the electrostatic latent image on the photoreceptor ₁ , which is a latent image holding member on which an electrostatic latent image has been formed, is developed by rotating it in the direction (the photoreceptor 1 is in the direction B) and developing the electrostatic latent image on the photoreceptor 1, which is a latent image holding member on which an electrostatic latent image has been formed, at the opposing position of the N1 pole. A good developed image was obtained.

It should be noted that, among the members in FIG. 6, those that are the same as those in FIG. 1 are given the same reference numerals. In addition, when the toner layer on the sleeve 3 is formed thinner than the shortest distance between the photoreceptor 1 and the sleeve 3 by the cooperative action of the magnetic blade 6 and the magnetic pole S ₁ to perform jumping development, a bias Power supply 7 is JP-A-55-
It is preferable to use the alternating power supply described in Nos. 18656-9 or JP-A-55-144254-5.

Embodiment 3 In the present invention, the magnet pieces 2a to 2d are further arranged as shown in FIG.
d, 2b and 2c repel each other at their adjacent surfaces 13,14. The surface magnetic flux densities of N ₁ pole and S ₁ pole are mainly formed by magnet pieces 2a and 2, respectively.
In addition to the magnetic force caused by b, the easy magnetization axes of the adjacent magnet pieces 2d and 2c are almost perpendicular to the adjacent surfaces 13 and 14, so that the seventh
A complementary pole effect is obtained as shown in Figure b. So N ₁・S ₁
A maximum surface magnetic flux of 1200G was obtained for both poles. When the magnet roll 2 thus prepared was developed using the N ₁ pole as the developing magnetic pole and the S ₁ pole as the opposing magnetic pole of the magnetic blade 6 in FIG. 6, a good developed image could be obtained. did it.

Reference Example Although it is not the embodiment of the present invention shown in FIG. It can generate a strong magnetic field as shown in . This is because the respective magnet pieces are joined against the mutually repelling force on the adjacent surfaces 15 to 18, and the lines of magnetic force generated approximately along the orientation direction of the easy magnetization axis of each magnet piece are respectively ₁・S ₁・N ₂・S This is because it is strengthened at the _two poles. In this way, a surface magnetic flux density of 1200G can be obtained at each magnetic pole, and the magnetic force is not repelled on the adjacent surfaces of the magnetic pieces, and the magnetic flux density pattern is half as large as the comparative example shown in Figure 3, which has no interpolation effect. A narrow value range (width at half the peak value of magnetic flux density) was obtained.

Embodiment 5 As another embodiment of the present invention, a case of a small-diameter magnet roll with a magnet outer diameter of 20 mm or less will be described. In such small-diameter magnet rolls, the magnet shaft occupies a large volume ratio, making it extremely difficult to design a magnet roll containing a polymer compound that has a magnetic flux density that can be used for electrophotography, etc. . In this case, it is rather rare that all magnetic poles need to be strong, so
By arranging the magnet pieces to strengthen only specific magnetic poles, a practical magnet roll can be obtained.

As shown in Figure 9a, attach the magnet piece 2 so that the outer diameter of the magnet roll is 18 mm with respect to the shaft 9 with a diameter of 6 mm.
A to 2d were arranged and adhered as shown in the figure. The magnetic easy axis of the magnetic material in each magnet piece was oriented as shown in FIG. 9a. At the adjacent surfaces 19, 20, the magnetic pieces 2a, 2c are bonded to the magnetic piece 2b against repulsive force, respectively, and since the magnetic easy axis is almost perpendicular to the adjacent surfaces 19, 20, the magnet Since the lines of magnetic force passing through the pieces 2a and 2c pass through the magnet piece 2b, a commutating effect for the _N1 pole is obtained as shown in FIG. 9b.
In the present invention, the magnetic piece 2d is also different from the N ₁ pole (S ₂ pole) by making the magnetic easy axis of the N ₂ pole orthogonal to _the adjacent surface ₃₃ . Because magnetic lines of force are generated, the N ₁ pole can be made even stronger.

In this way, despite the small diameter of the magnet roll, it is possible to obtain a surface magnetic flux density of 1200G for N ₁ pole, and it can be used as the developing magnetic pole of a magnet roll for developing electrophotography. Summer. This example is an example in which only one pole (N ₁ pole) of a small diameter magnet roll is strengthened.
Even in the case of the other embodiments described above, depending on the strength of the required magnetic flux density, even an outer diameter of 20 mm or less can be sufficiently put into practical use.

When configured so that the magnets repel each other on the adjacent surfaces of each magnet as described above,
Concentration of magnetic lines of force occurs in the repelling part, and a strong magnetic field can be generated. Furthermore, by making the direction of magnetization of the magnetic piece of the commutating pole substantially orthogonal to the surface adjacent to the main pole, the magnetic flux density of the main pole can be increased by about 15 to 25%. Furthermore, in a configuration in which the magnet piece is an anisotropic magnet and the axis of easy magnetization of the magnet piece is made almost perpendicular to the adjacent surface, the maximum energy product is smaller than that of a conventional sintered magnet. It has also become possible to obtain magnet rolls that are sufficiently useful for electrophotography.

In the present invention, in order to bond the magnet pieces to the support shaft so as to repel each other, a strong adhesive called epoxy or rubber bond or instant adhesive is used as the adhesive. In addition, it is preferable to cover the surface of the roller 2 with a synthetic resin or the like so that the magnet pieces 2a to 2d after adhesion do not become separated due to their repulsive force.The most suitable coating material is polyester, polyethylene, etc. Shrinkable tube made of thermoplastic resin such as polypropylene (Figure 9a)
21).

The magnetic roller according to the present invention can be used not only in a developing device but also as a magnetic roller in a cleaning device, other image forming devices, and recording devices.

In the explanation of the embodiment, an example was shown in which a magnetic piece was bonded to a support shaft with a circular cross-section to make a magnetic roller with a circular cross-section as a whole, but the shaft and the magnetic roller are not limited to circular shapes. It may have a polygonal shape.

As described above in detail, according to the present invention, it is possible to obtain a magnet roll that is small in size and has strong magnetic force.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional developing device, Fig. 2 is a perspective view of a magnet roll, Figs. b is a side view of the magnet roll according to the present invention and an explanatory diagram of magnetic field lines; Fig. 5a,
b, Figures 7a and b, and Figures 9a and b are side views and explanatory diagrams of magnetic lines of force of magnet rolls showing other embodiments of the present invention, respectively, and Figure 6 is a diagram to which the magnet roll of the present invention is applied. FIG. 3 is a cross-sectional view of the developing device. FIGS. 8a and 8b are explanatory diagrams of reference examples. In the figure, 1... Photoreceptor, 2... Magnet roller, 2a to 2d... Magnet piece, 3... Sleeve, 4... Magnetic toner, 9... Support shaft, 10
~20...represents an adjacent surface.

Claims (1)

[Claims] 1. In a magnet roll formed by fixing a plurality of magnets to a support shaft, each magnet has magnetic anisotropy, and at least one set of adjacent magnets among each magnet has magnetic anisotropy. The magnets are each magnetized so as to have a magnetic pole on the surface of the magnet roll, and at least one set of adjacent magnets is arranged so that the magnetic forces of the respective magnets repel each other on the adjacent surfaces. A magnet roll characterized in that the magnets are arranged and bonded so that the direction of the axis of easy magnetization of the magnets is substantially perpendicular to adjacent surfaces of both magnets. 2. The magnet roll according to claim 1, wherein the magnet is a rubber magnet or a plastic magnet. 3. Claim 1, characterized in that the magnet roll is covered with a shrinkable tube.
The magnetrol according to item 1 or 2. 4. A magnet roll formed by fixing a plurality of magnets to a support shaft, each magnet having magnetic anisotropy, and at least one set of adjacent magnets among each magnet having magnetic anisotropy. The magnet roll is magnetized so as to have a magnetic pole on its surface, and the at least one set of adjacent magnets is arranged such that one magnet is easily magnetized so that the magnetic forces of the respective magnets repel each other on the adjacent surfaces. A magnet roll is arranged and bonded so that the direction of its axis is almost perpendicular to the adjacent surfaces of both magnets. A developing device comprising: a developer carrying member for transporting to a developing position where an image is developed; and a developer storage means for supplying developer to the developer carrying member. 5. The magnet roll according to claim 4, wherein the magnet is a rubber magnet or a plastic magnet.